Stromal cell derived factor-1 (SDF-1, or CXCL12) is a 68 amino acid member of the chemokine family which attracts resting T-lymphocytes, monocytes and CD34+ stem cells. It is commonly found in two different forms SDF-1α and SDF-1β which are the result of differential mRNA splicing (U.S. Pat. No. 5,563,048). These forms are essentially the same except that SDF-1β is extended by four amino acids (-Arg-Phe-Lys-Met) at the C terminus. Both forms of SDF-1 are initially made with a signal peptide, 21 amino acids in length, that is cleaved to make the active peptide (U.S. Pat. No. 5,563,048). For the purposes of the present invention, it will be understood that the term “SDF-1” refers to the active form of the peptide, i.e., after cleavage of the signal peptide, and encompasses both SDF-1α and SDF-1β.
It has also been shown that the full length, 68 amino acid, SDF-1 sequence is not needed for activity. Peptides that have at least the first eight N-terminal residues of SDF-1 maintain the receptor binding and bioactivity of the full peptide, albeit at a reduced potency. For example, SDF-1, 1-8, 1-9, 1-9 dimer, and 1-17 induce intracellular calcium and chemotaxis in T lymphocytes and CEM cells and bind to CXC chemokine receptor 4 (CXCR4). However, native SDF-1 has half-maximal chemoattractant activity at 5 nM, whereas the 1-9 dimer requires 500 nM and is therefore 100-fold less potent. The 1-17 and a 1-9 monomer analogs are 400- and 3600-fold, respectively, less potent than SDF-1. SDF-1 variants with C-terminal cyclization have been described that have a higher CXCR4 receptor binding affinity and cyclization of this type may, if desired, be used in connection with the peptides described herein. For the purposes of the present invention, the term SDF-1 will include forms of the peptide that have been truncated at the C terminal end but which maintain SDF-1 biological activity, i.e., which are chemotactic for T lymphocytes and CEM cells and which bind to CXC chemokine receptor 4 (CXCR4). At a minimum, these truncated forms include the first eight amino acids at the N-terminal end of the peptide.
SDF-1 plays a key-role in the homing of hematopoietic stem cells to bone marrow during embryonic development (Nagasawa, et al., Nature 382:635-638 (1996); Zou, et al., Nature 393:595-599 (1998)) and after stem cell transplantation (Lapidot, et al., Blood 106:1901-1910 (2005)). In addition to its role in stem cell homing, SDF-1 is also important in cardiogenesis and vasculogenesis. SDF-1 deficient mice die perinatally and have defects in cardiac ventricular septal formation, bone marrow hematopoiesis and organ-specific vasculogenesis (Nagasawa, et al., Nature 382:635-638 (1996); Zou, et al., Nature 393:595-599 (1998)). It has also been reported that abnormally low levels of SDF-1 are at least partially responsible for the impaired wound healing associated with diabetic patients and that impairment can be reversed by the administration of this cytokine at the site of tissue damage (Gallagher, et al., J. Clin. Invest. 117:1249-1259 (2007)).
In the normal adult heart, SDF-1 is expressed constitutively, but expression is upregulated within days after myocardial infarction (Pillarisetti, et al., Inflammation 25:293-300 (2001)). Askari et al. increased SDF-1 expression 8 weeks after myocardial infarction by intramyocardial transplantation of stably transfected cardiac fibroblasts overexpressing SDF-1 in combination with G-CSF therapy (Lancet 362:697-703 (2003)). This was associated with higher numbers of bone marrow stem cells (c-Kit or CD34 positive) and endothelial cells in the heart and resulted in an increase of vascular density and an improvement of left ventricular function. These studies suggest that the insufficiency of the naturally-occurring myocardial repair process may be in part due to inadequate SDF-1 availability. Hence, the delivery of SDF-1 in a controlled manner after myocardial infarction may attract more progenitor cells and thereby promote tissue repair (Penn, et al., Int. J. Cardiol. 95(Suppl. 1):S23-S25 (2004)). Apart from this, the administration of SDF-1 may be used to improve the healing of wounds or ulcers in patients, especially those with diabetes.
One way that may be used for the sustained delivery of drugs at a site of tissue damage is through the use of biologically compatible membranes. Certain peptides are capable of self-assembly when incubated in the presence of a low concentration of monovalent metal cation (U.S. Pat. No. 5,670,483; U.S. Pat. No. 6,548,630). Assembly results in the formation of a gel-like membrane that is non-toxic, non-immunogenic and relatively stable to proteases. Once formed, membranes are stable in serum, aqueous solutions and cell culture medium. They can be made under sterile conditions, are capable of supporting the growth of cells and are slowly digested when implanted in an animal's body. These characteristics make the membranes well suited as devices for the delivery of therapeutic agents (US 20060148703 and 20060088510).